Leadless semiconductor package and manufacturing method thereof

ABSTRACT

A leadless semiconductor package mainly includes a semiconductor device securely attached to an upper surface of a die pad by solder paste and a plurality of leads arranged about the periphery of the die pad. The thickness of the leads and the die pad are within a range of 10 to 20 mils. The semiconductor device is electrically coupled to one of the leads. A package body is formed over the semiconductor device and the leads in a manner that the lower surfaces of the die pad and the leads are exposed through the package body. Preferably, the first semiconductor device is electrically coupled to one of the leads by at least one heavy gauge aluminum wire. The present invention further provides a method of producing the semiconductor package described above.

RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 10/811,857, filed Mar. 30, 2004 now U.S. Pat. No.7,053,469.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to lead frame packages, and more specifically toleadless semiconductor packages and manufacturing methods thereof.

2. Description of the Related Art

Lead frame packages have been used for a long period of time in the ICpackaging history mainly because of their low manufacturing cost andhigh reliability. However, as integrated circuits products move itsendless pace toward both a faster speed and a smaller size, thetraditional lead frame packages have become gradually obsolete for somehigh performance-required packages. Thus BGA (Ball Grid Array Packages)and CSP (Chip Scale Package) have emerged and become increasinglypopular as a new packaging choice. The former has been widely used in ICchips that have higher I/Os and need better electrical and thermalperformance than the conventional packages such as CPU and graphicchips. The latter has been widely used in mobile products of which thefootprint, package profile and package weight are major concerns.

However, the lead frame package still remains its market share as acost-effective solution for low I/O ICs. Traditional lead frame packagehas its limit of providing a solution for chip scale and low profilepackage due to the long inner leads and outer leads. Therefore, thesemiconductor packaging industry develops a leadless package withoutouter leads such that both the footprint and the package profile can begreatly reduced. FIGS. 1 and 2 show a leadless package 10 wherein theleads 11 a are disposed at the bottom of the package as compared to theconventional gull-wing or J-leaded type package. The die pad 11 b of theleadless package 10 is exposed from the bottom of the package therebyproviding better heat dissipation. Typically, there are four tie bars 11c being connected to the die pad 11 b. The leadless package 10 includesa chip 12 sealed in a package body 13. The active surface of the chip 12is provided with a plurality of bonding pads (not shown) electricallyconnected to the leads 11 a via wire bonding.

Due to the elimination of the outer leads, leadless packages arefeatured by lower profile and weight. Furthermore, the leadless package10 is also a cost-effective package due to its use of existing BOM (billof materials). All the above-mentioned properties make the currentleadless packages very suitable for telecommunication products such ascellular phones, portable products such as PDA (personal digitalassistant), digital cameras, and IA (Information Appliance).

As the performance requirements for computers and other electronicapparatuses increase, the semiconductor devices operate at higher powerand are manufactured at increased device densities. As a result, greateremphasis has been placed on the thermal performance of the semiconductordevices. However, currently available leadless packages fail to meet thehigh power dissipation requirements of automotive, industrial, andcommercial applications.

SUMMARY OF THE INVENTION

The present invention therefore provides a leadless semiconductorpackage designed to meet the high power dissipation requirements ofautomotive, industrial, and commercial applications.

Accordingly, in a first aspect, the present invention provides asemiconductor package mainly including a first semiconductor device(such as a power semiconductor device) securely attached to an uppersurface of a first die pad by solder paste and a plurality of leadsarranged about the periphery of the first die pad. The thickness of theleads and the die pads are within a range of about 10 mils to about 20mils. The first semiconductor device is electrically coupled to one ofthe leads. A package body is formed over the semiconductor devices andthe leads in a manner that the lower surfaces of the die pad and theleads are exposed through the package body. Preferably, the firstsemiconductor device is electrically coupled to one of the leads by atleast one heavy gauge aluminum wire.

The semiconductor package may further include a second semiconductordevice (such as a control semiconductor device) securely attached to asecond die pad by silver epoxy. The second semiconductor device iselectrically coupled to the leads and the first semiconductor device bya plurality of gold wires.

The package of the present invention can be mounted onto a PC board withthe die pads soldered directly to a matching thermal land on the PCboard thereby providing a low thermal-impedance path to carry heatgenerated from the semiconductor devices mounted on the die pads. Theuse of 10-20 mils thick die pads and heavy gauge aluminum bond wireshelps transfer heat from the package while providing low electricalon-resistance.

According to a second aspect of the invention, there is provided aprocess for making a plurality of semiconductor packages. The methodcomprises the steps of: (A) providing a lead frame having a thicknessbetween about 10 mils and about 20 mils, the lead frame including aplurality of units in an array arrangement, each unit having a first diepad and a plurality of leads arranged at the periphery of the first diepad, each lead having an half-etched indentation formed corresponding toa predetermined dicing line; (B) attaching a first semiconductor deviceonto the first die pad of each unit of the lead frame by solder paste;(C) electrically coupling the first semiconductor devices to the leads;(D) forming a molded product by encapsulating the first semiconductordevices against the lead frame to form a plurality of package bodieseach encapsulating one of the first semiconductor devices; and (E)cutting the molded product along the half-etched indentations of theleads into individual semiconductor packages by a punch singulation.

BRIEF DESCRIPTION OF THE DRAWING

Other objects, advantages, and novel features of the invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawings.

FIG. 1 is a bottom view of a conventional leadless package;

FIG. 2 is a cross-sectional view of the package of FIG. 1;

FIG. 3 is a top plan view of a portion of a lead frame according to oneembodiment of the present invention;

FIG. 4 is a top plan view of a leadless semiconductor package accordingto one embodiment of the present invention wherein the package body isremoved; and

FIG. 5 is a cross-sectional view of the package of FIG. 4 before a punchsingulation step is conducted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows a top plan view of a portion of a lead frame 100 accordingto one embodiment of the present invention. The lead frame 100 comprisesa plurality of units separated from each other by a plurality of dambars(not shown). Though only one unit of the lead frame 100 is shown in FIG.3, a lead frame for use with the invention can include any numbers ofunits that is compatible with the manufacturing equipment, e.g., mold,being used. The dambars generally form an orthogonal grid on the leadframe 100. The lead frame 100 is typically made of a copper-base alloyor made of copper or alloys containing copper. The lead frame 100 have athickness between about 10 mils and about 20 mils, and is shaped byetching in the manner that each unit of the lead frame 100 has aplurality of leads 110 and a power output bar 112 arranged about theperiphery of two die pads 120 and 122. In addition, a half-etchedoperation is conducted in the manufacturing process of the lead frame100. The half-etched regions on the lead frame 100 are hatched in FIG. 3to facilitate understanding. Noted that each lead 110 is half-etched atits bottom surface to form an indentation 110 a at a locationcorresponding to a predetermined dicing line (not shown). It is notedthat the “half-etch” herein does not mean only exactly removing a halfof the thickness of the lead frame through etching but also includes apartial etching for removing merely a part of the thickness of the leadframe. Lead frames suitable for use in the present invention areavailable in three lead finishes: post plated SnPb and Matte Sn, and preplated Ni/Pd with flash of Au (i.e., PPF (Pre-Plating Lead Frame)).

FIG. 4 shows a leadless semiconductor package 200 according to oneembodiment of the present invention. The package 200 mainly includes acontrol semiconductor device 130 securely attached to an upper surfaceof the die pad 120 by silver epoxy and a power semiconductor device 132securely attached to an upper surface of the die pad 122 by solder pastewhich provides good electrical and thermal conductivity. Suitable solderpaste is a conductive solder alloy containing Sn, Pb, Bi, In, Ag, Au. Ina preferred embodiment the solder paste is Sb/Sn based solder with 80%to 97% Sn and the balance mostly Sb. The power semiconductor device 132may be a high power die to be used in a power amplifier (PA) and thecontrol semiconductor device 130 may be a control die including acontrol circuitry needed to perform responsive control of the powersemiconductor device. The control semiconductor device 130 areelectrically coupled to the leads 110 and the power semiconductor deviceby a plurality of gold wires 140. The power semiconductor device 132 iselectrically coupled to the power output bar 112 by heavy gauge aluminumwires 142 (preferably 5-15 mils).

Referring to FIG. 5, a package body 150 is formed over the leads 110,the bar 120, the die pads 120, 122 and the semiconductor devices 130,132. The lower surfaces of the leads 110, the bar 120, and the die pads120, 122 are exposed from the bottom of the package body 150. Thethickness of them are preferably within a range of 10 to 20 mils therebyincreasing the area of the interface between the package body 150 andthe die pads 120, 122 as well as the leads 110, and prolonging the pathand time for moisture diffusion into the package 200. Furthermore, thedie pads 120 and 122 are half-etched to form indentations 120 a and 122a thereby significantly enhancing the “locking” of the die pad 120 and122 in the package body 150.

The package 200 can be mounted onto a substrate, such as a printedcircuit board (PC board), like other leadless devices. The die pads 120and 122 are soldered directly to a matching thermal land on the PC boardthereby providing a low thermal-impedance path to carry heat generatedfrom the semiconductor devices mounted on the die pads 120 and 122. Inthe package 200, conduction is the primary modes of heat transfer thatmoves the generated heat away from the devices 130, 132 and out of thepackage through exposed die pads 120 and 122 on the bottom surface ofthe package thereby greatly enhancing the thermal performance of thepackage. The use of 10-20 mils thick die pads and heavy gauge aluminumbond wires helps transfer heat from the package while providing lowelectrical on-resistance. Therefore, the leadless semiconductor packageof the present invention overcomes the limitations of existing powerpackages, and meets the high power dissipation requirements ofautomotive, industrial, marine, and commercial applications.

Although the present invention is discussed in detail with respect tothe leadless semiconductor package 200 with two semiconductor devices, aleadless semiconductor package with only one semiconductor device isstill considered within the spirit and scope of the invention.

The present invention further provides a process for making theaforementioned leadless semiconductor package. Firstly, in each unit ofthe lead frame 100, a control semiconductor device 130 is attached tothe die pad 120 through silver epoxy and a power semiconductor device132 is attached to the die pad 122 through solder paste. Preferably, apolyimide (PI) tape (not shown) is attached onto the lower surface ofthe lead frame 100, and this is to prevent the mold flash problem in themolding process. After that, a regular wire-bonding process is performedto make Au wire interconnections between the control semiconductordevice 130 and the leads 110 of the lead frame 100 as well as the powersemiconductor device 132 (see FIG. 4). In addition, Al wire bondingbetween the power semiconductor device 132 and the power output bar 112(see FIG. 4) is performed using an ultrasonic aluminum wedge bonder.

Then, referring to FIG. 5, a molded product is formed by encapsulatingthe control semiconductor devices 130 and the power semiconductordevices 132 against the lead frame 100 to form a plurality of packagebodies (only one shown in FIG. 5) each encapsulating one of the controlsemiconductor devices 130 and one of the power semiconductor devices132.

Thereafter, a singulation step is conducted to cut the aforementionedmolded product into individual leadless semiconductor packages. Sincethe lead frame 100 have a thickness between about 10 mils and about 20mils, the singulation step is conducted by cutting at the half-etchedregions on the lead frame 100, e.g., the indentations 110 a of the leads110, so as to enhance the package integrity. When an individual moldingprocess is used to form the molded product, the singulation step isconducted by a punching operation. Alternatively, when an overmoldingprocess is used to form the molded product, the singulation step isconducted by sawing the molded product from the lower surface (fromwhich one surfaces of the die pads 120, 122 and the leads 110 areexposed) thereof to the upper surface thereof.

Although the invention has been explained in relation to its preferredembodiment, it is to be understood that many other possiblemodifications and variations can be made without departing from thespirit and scope of the invention as hereinafter claimed.

1. A process for making a plurality of semiconductor packages,comprising the following steps: providing a lead frame having athickness between about 10 and about 20 mils, the lead frame including aplurality of units in an array arrangement, each unit having first andsecond die pads, and an output bar and a plurality of leads arranged atthe periphery of the die pads, each lead having an half-etchedindentation formed corresponding to a predetermined dicing line;attaching a first semiconductor device onto the first die pad of eachunit of the lead frame by solder paste; attaching a second semiconductordevice onto the second die pad of each unit of the lead frame by silverepoxy; electrically coupling the first semiconductor device to theoutput bar; electrically coupling the second semiconductor device to theleads and the first semiconductor device; forming a molded product byencapsulating the semiconductor devices against the lead frame to form aplurality of package bodies each encapsulating the first semiconductordevice and the second semiconductor device; and cutting the moldedproduct along the half-etched indentations of the leads into individualsemiconductor packages.
 2. The process as claimed in claim 1, whereinthe first semiconductor device is electrically coupled to the output barby at least one heavy gauge aluminum wire.
 3. The process as claimed inclaim 1, wherein the second semiconductor device is electrically coupledto the leads and the first semiconductor device by a plurality of goldwires.
 4. The process as claimed in claim 1, wherein the firstsemiconductor device is a power semiconductor device and the secondsemiconductor device is a control semiconductor device.
 5. The processas claimed in claim 1, wherein the cutting step comprises a step ofsawing the molded product into individual semiconductor packages.
 6. Theprocess as claimed in claim 1, wherein the molded product has opposingupper and lower surfaces, one surfaces of the die pads and the leads areexposed from the lower surface of the molded product and the cuttingstep comprises a step of sawing the molded product into individualsemiconductor packages from the lower surface of the molded product tothe upper surface of the molded product.
 7. The process as claimed inclaim 1, wherein the cutting step comprises a step of punching themolded product into individual semiconductor packages.